deep surface of the mandible. In the higher Primates the conditions are more complex, there being posterior and anterior bellies.
The deltoid muscle is strong, but the pectoralis major, with which it is fused at its insertion into the pectoral crest on the humerus, is weaker than in many of the Primates. There is no clavicular origin of the pectoralis major as in the quadrupedal, terrestrial Baboons. The muscles arising from the scapular surfaces are not-peculiar.
The fascial sheath of the latissimu* dorsi gives rise to two slips, which unite to form the dorso-epitrochlearis muscle. This climbing muscle, which is inserted into the olecranon and fascia over the internal epicondyle, is present in all Primates except Man, in whom it is merely represented by some fascia. The biceps has a well-marked lacertus fibrosus, and the coraco-brachialis is double, the musculo-cutaneous nerve passing between the two parts.
The muscles of the forearm exhibit an early stage in the evolution of the flexors of Man. The flexor sub-limis and flexor profundus digitorum exhibit some fusion, and the flexor longus pollicis is not separated from the deep flexor mass. The stages in the evolution of the human flexor muscles are described on p. 187. There is no extensor brevis pollicis.
The gluteus maximus, whose origin extends backwards from the posterior superior iliac spine, is thinner at its insertion into the femoral shaft.
The biceps has a single long head only, the short head being absent as in some lower Mammals. It is inserted into the deep fascia of the leg, no fibres going to the